1. Technical Field
The present invention relates to a toroidal continuously variable transmission unit which can be used as a transmission unit for automotive vehicles or various types of industrial machines.
2. Background Art
A double cavity toroidal variously variable transmission unit for use in, for example, an automotive vehicle is configured as is shown in FIGS. 14 and 15. As is shown in FIG. 14, an input shaft (a rotational center axis) 1 is supported rotatably inside a casing 50, and two input-side discs 2, 2 and two output-side discs 3, 3 are attached to an outer circumference of the input shaft 1. In addition, an output gear 4 is supported rotatably on an outer circumference of an intermediate portion of the input shaft 1. The output-side discs 3, 3 are spline connected to tubular flange portions 4a, 4a which are provided at a central portion of the output gear 4.
The input shaft 1 is made to be driven to rotate by a drive shaft 22 via a loading cam type pressing device 12 which is provided between an input-side disc 2 shown as being situated on a left-hand side in the figure and a cam plate (a loading cam) 7. In addition, the output gear 4 is supported relative to a partition wall (an intermediate wall) 13 which is made up by connecting together two members via angular bearings 107 and is supported inside the casing 50 via the partition wall 13, whereby the output gear 4 can not only rotate about an axis O of the input shaft 1 but also is prevented from being displaced in the direction of the axis O.
The output-side discs 3, 3 are supported by needle bearings 5, 5 which are interposed between the input shaft 1 and themselves so as to rotate about the axis O of the input shaft. In addition, the left-hand input-side disc 2 in the figure is supported on the input shaft 1 via a ball spline 6, and a right-hand input-side disc 2 is spline connected to the input shaft 1, whereby these input-side discs 2 are made to rotate together with the input shaft 1. In addition, power rollers 11 (refer to FIG. 15) are held rotatably between internal surfaces (toroidal surfaces; also referred to as traction surfaces) 2a, 2a of the input disc 2, 2 and internal surfaces (toroidal surfaces; also referred to as traction surfaces) 3a, 3a of the output disc 3, 3.
A stepped portion 2b is provided on an inner circumferential surface 2c of the input-side disc 2 which is depicted as being situated on the right-hand side as viewed in FIG. 14, and a stepped portion 1b formed on an outer circumferential surface 1a of the input shaft 1 is brought into striking contact with the stepped portion 2b, while a back side (a right-hand side as viewed in FIG. 14) of the input-side disc 2 is brought into striking contact with a loading nut 9 screwed on a threaded portion formed on the outer circumferential surface of the input shaft. By this configuration, the displacement of the input-side disc 2 in the direction of the axis O relative to the input shaft 1 is prevented substantially. In addition, a coned disc spring 8 is provided between the cam plate 7 and a flange portion 1d of the input shaft 1, and this coned disc spring 8 imparts a pressure to abutment portions between the toroidal surfaces 2a, 2a, 3a, 3a of the respective discs 2, 2, 3, 3 and circumferential surfaces 11a, 11a of the power rollers 11, 11.
As is shown in FIG. 15, which is a sectional view taken along the line A-A in FIG. 14, a pair of yokes 23A, 23B are supported inside the casing 50 and in positions lying sideways of the output-side discs 3, 3 so as to hold both the discs 3, 3 from both sides thereof. The pair of yokes 23A, 23B are formed by pressing or forging a metal such as steel into a rectangular shape. In addition, to support rotatably pivot shafts 14 provided at both end portions of trunnions 15, which will be described later, circular support holes 18 are provided in four corners of the yokes 23A, 23B, and circular locking holes 19 are formed in central portions in a width direction of the yokes 23A, 23B.
The pair of the yokes 23A, 23B are supported by support posts 64, 68 formed at portions on inner surfaces of the casing 50 which oppositely face each other so as to oscillate about the support posts 64, 68 as fulcrums. These posts 64, 68 are provided, respectively, in a first cavity 221 and a second cavity 222 which exist between the internal surface 2a of the input-side disc 2 and the internal surface of the output-side disc 3 so as to face oppositely each other.
Consequently, the yokes 23A, 23B face oppositely at one end portions thereof an outer circumferential portion of the first cavity 221 and at the other end portions thereof an outer circumferential portion of the second cavity 222 in such a state that the yokes 23A, 23B are supported by the support posts 64, 68, respectively.
Since the first and second cavities 221, 222 have the same construction, hereinafter, only the first cavity 221 will be described.
As is shown in FIG. 15, in the inside of the casing 50, a pair of trunnions 15, 15 are provided in the first cavity 221 which each oscillate about a pair of pivot shafts (attitude shafts) 14, 14 which lie in positions which are twisted relative to the input shaft 1. In addition, in FIG. 15, the illustration of the input shaft 1 is omitted. The trunnions 15, 15 each have a pair of bent wall portions 20, 20 which are formed at both longitudinal (vertical in FIG. 15) end portions of a support plate portion 16 which constitutes a main body portion thereof so as to be bent towards an internal surface side of the support plate portion 16. In addition, a pocket portion P which is a recessed accommodation space for accommodating the power roller 11 is formed in each of the trunnions 15, 15 by these bent wall portions 20, 20. In addition, the pivot shafts 14, 14 are provided coaxially with each other on external surfaces of the respective bent wall portions 20, 20.
A circular hole 21 is formed in a central portion of the support plate portion 16, and a proximal end portion (a first shaft portion) 23a of a displacement shaft 23, which acts as a support shaft which supports the trunnion 15 rotatably, is supported in this circular hole 21. In addition, the inclination angles of the displacement shafts 23 which are supported at central portions of the trunnions 15, 15 are made to be adjusted by oscillating the trunnions 15, 15 about their associated pivot shafts 14, 14. Additionally, each power roller 11 is supported rotatably on a circumference of a distal end portion (a second shaft portion) 23b of the displacement shaft 23 which projects from an internal surface of each of the trunnions 15, 15, and the power rollers 11, 11 are held between each of the input-side discs 2, 2 and each of the output-side discs 3, 3. Note that the proximal end portion 23a and the distal end portion 23b of each of the displacement shafts 23, 23 are offset from each other.
In addition, as has been described before, the pivot shafts 14, 14 of each of the trunnions 15, 15 are supported so as to oscillate freely and to be displaced axially (vertically in FIG. 15) relative to the pair of yokes 23A, 23B, and the horizontal movement of the trunnions 15, 15 is restricted by the respective yokes 23A, 23B. As has been described before, the circular four support holes 18 are formed in the four corners of each of the yokes 23A, 23B, and the pivot shafts 14 which are provided at both the end portions of the trunnion 15 are supported in the support holes 18, respectively, via radial needle bearings (attitude bearings) 30 so as to freely oscillate (freely tilt). In addition, as has been described before, the circular locking holes 19 are formed in the central portion in the width direction (horizontal in FIG. 15) of the yokes 23A, 23B, and inner circumferential surfaces of the locking holes 19 are made into a shape of an inner surface of a circular tube so that the support posts 64, 68 are fitted therein, respectively. Namely, the upper yoke 23A is supported in an oscillating fashion by the spherical post 64 which is supported on the casing 50 via a fixing member 52, and the lower yoke 23B is supported in an oscillating fashion by the spherical post 68 and an upper cylinder body 61 of a drive cylinder 31 which supports the spherical post 68.
The displacement shafts 23, 23 provided on the trunnions 15, 15 are provided in 180-degree opposite positions relative to the input shaft 1. In addition, the direction in which the distal end portions 23b of the displacement shafts 23, 23 are offset relative to the proximal end portions 23a is made to be the same (vertically opposite in FIG. 15) as the rotational direction of both the discs 2, 2, 3, 3. In addition, the offset direction is made to be substantially at right angles to the direction in which the input shaft 1 is provided. Consequently, the respective power rollers 11, 11 are supported so as to be slightly displaced in a longitudinal direction of the input shaft 1. As a result of this, even in the event that the power rollers 11, 11 tend to be displaced in the axial direction of the input shaft 1 due to elastic deformation or the like of respective constituent members based on a thrust load generated by the pressing device 12, the displacement of the power rollers 11, 11 is absorbed with no unreasonable force applied to the respective constituent members.
In addition, a thrust ball bearing (a thrust bearing) 24, which is a thrust rolling bearing, and a thrust needle bearing 25 are provided between an external surface of the power roller 11 and an internal surface of the support plate portion 16 of the trunnion 15 sequentially in that order from the external surface of the power roller 11. Of these bearings, the thrust ball bearing 24 is such as to permit the rotation of each power roller 1 while bearing a load applied to the power roller 11 in a thrust direction. The thrust ball bearing 24 designed in that way is made up of a plurality of balls (rolling elements) 26, 26, an annular cage 27 for holding these balls 26, 26 in a rolling fashion, and an annular outer ring 28. In addition, an inner ring raceway of the thrust ball bearing 24 is formed on the external surface (a large end surface) of the power roller 11, while an outer ring raceway is formed on an internal surface of the outer ring 28.
In addition, the thrust needle bearing 25 is held between the internal surface of the support plate portion 16 of the trunnion 15 and an external surface of the outer ring 28. The thrust needle bearing 25 designed in this way permits the oscillation of the power roller 11 and the outer ring 28 about the proximal end portion 23a of the displacement shaft 23 while bearing a thrust load applied to the outer ring 28 from the power roller 11.
Furthermore, drive rods (shaft portions extending from the pivot shaft 14) 29, 29 are provided at one end portions (lower end portions in FIG. 15) of the respective trunnions 15, 15, and drive pistons (hydraulic pistons) 33, 33 are fixedly provided on outer circumferential surfaces of intermediate portions of the respective drive rods 29, 29. In addition, these drive pistons 33, 33 are fluid tightly fitted in the drive cylinder 31 which is made up of the upper cylinder body 61 and a lower Cylinder body 62. The drive pistons 33, 33 and the drive cylinder 31 make up a drive system 32 for displacing the respective trunnions 15, 15 in the axial direction of the pivot shafts 14, 14 of the trunnions 15, 15.
In the case of the toroidal continuously variable transmission which is configured as has been described above, the rotation of the drive shaft 22 is transmitted to the respective input-side discs 2, 2 and the input shaft 1 via the pressing device 12. Then, the rotation of the input-side discs 2, 2 is transmitted, respectively, to the output-side discs 3, 3 via the pair of power rollers 11, 11, and furthermore, the rotation of the output-side discs 3, 3 is taken out from the output gear 4.
When a rotational speed ratio between the input shaft 1 and the output gear 4 is changed, the pair of drive pistons 33, 33 are made to be displaced in opposite directions to each other. The pair of trunnions 15, 15 are displaced (offset) in opposite directions to each other in conjunction with the displacement of the respective pistons 33, 33. For example, the left-hand power roller 11 in FIG. 15 is displaced downwards, while the right-hand power roller 11 in the same figure is displaced upwards in the figure. As a result, directions of tangential forces are changed which act on the abutment portions between the circumferential surfaces 11a, 11a of the respective power rollers 11, 11 and internal surfaces 2a, 2a, 3a, 3a of the respective input-side discs 2, 2 and respective output-side discs 3, 3. Then, in conjunction with the changes in the tangential forces, the respective trunnions 15, 15 oscillate (tilt) about the pivot shafts 14, 14 which are rotatably supported on the yokes 23A, 23B in opposite directions to each other.
As a result of the oscillation of the trunnions 15, 15, abutment positions between the circumferential surfaces (truncation surfaces) 11a, 11a of the respective power rollers 11, 11 and the respective internal surfaces 2a, 3a change, whereby the rotational speed ratio between the input shaft 1 and the output gear 4 changes. In addition, when a torque transmitted between the input shaft 1 and the output gear 4 changes, resulting in a change in elastic deformation amount of the respective constituent members, the respective power rollers 11, 11 and the outer rings 28, 28 which are attached to the power rollers 11, 11 slightly rotate about the proximal end portions 23a, 23a of the respective displacement shafts 23, 23. Since the thrust needle bearings 25, 25 are present, respectively, between external surfaces of the respective outer rings 28, 28 and internal surfaces of the support plate portions 16 which constitute the trunnions 15, 15, the rotation is implemented smoothly. Consequently, only a small magnitude of force is necessary to change the inclination angles of the respective displacement shafts 23, 23.
Incidentally, in the toroidal continuously variable transmission unit which has the configuration described above, as has been described above, the distal end portion 23b and the proximal end portion 23a of the displacement shaft 23 which supports the power roller 11 are offset from each other so that the power roller 11 oscillates relative to the trunnion 15 so as to transmit smoothly the pressing force from the input-side disc 2 to the output-side disc 3. Namely, the rotational axis of the power roller 11 (the distal end portion 23b of the displacement shaft 23) is offset relative to the support shaft (the proximal end portion 23a of the displacement shaft 23) which supports rotatably the power roller 11 relative to the trunnion 15, that is, an axis of the inner hole 21. This will be true also in a construction where an outer ring 28 is integrated with a displacement shaft 23 as is shown in FIG. 16.
In a construction like this, however, the machining cost inevitably has to be increased to realize the offset configuration of the displacement shaft 23. In addition, the reduction in size and weight of the trunnion 15 is disrupted due to a restriction imposed by the offset configuration. Furthermore, since the bearing which bears the thrust load starts to perform a slipping motion due to the oscillating and rotating actions round the displacement shaft 23 of the power roller 11 and the like, there is caused a problem that oscillating resistance is increased.
To cope with this problem, conventionally, techniques have been proposed which avoid the offset in the shaft portion which rotatably supports the power roller 11 by the use of various devices. For example, in Patent Document No. 1, there is disclosed a construction in which an outer ring 28 is made to be guided slidingly relative to a trunnion 15 by supporting the outer ring 28 within a pocket portion P of the trunnion 15 so as to slide along an axial direction of an input shaft 1 by only a linear bearing which is interposed between the trunnion 15 and the outer ring 28.
In addition, in Japanese Patent Unexamined Publication No. JP-A-2004-138249 (JP '249)(FIG. 4), there is disclosed a construction flat surface portions are provided, respectively, on a supporting surface which faces a pocket portion P side of a support plate portion 16 of a trunnion 15 and an outer ring 28, and a roller bearing is interposed between these flat surface portions.
Furthermore, in the toroidal continuously variable transmission units described above, power transmission between the power rollers 11 and the input-side and the output-side discs 2, 3 is implemented in a non-contact fashion by virtue of a traction force applied via an oil film with a view to preventing damage to surfaces of those members. Because of this, a sufficient amount of lubrication oil (traction oil) as to form an oil film for transmission of torque in a non-contact fashion needs to be supplied a traction surface which is formed between the power roller 11 and the input-side and output-side discs 2, 3, and sufficient lubrication needs to be implemented on bearings which rotatably supports the discs 2, 3 and the power rollers 11 (hereinafter, also referred to as power roller bearings). Then, for example, in Japanese Patent Unexamined Publication No. JP-A-2004-324877 (JP '877)(Fig. 10), by mounting a mesh filter for a displacement shaft 23 on a power roller bearing so as to remove contaminants (foreign matters) immediately before a thrust ball bearing 24 which is subjected to a severe service condition, a good lubrication of the bearing is attempted to be implemented.
The problems with these arrangements are as follows.
In the construction disclosed in Japanese Patent Unexamined Publication No. JP-A-7-198014 (JP '014), however, since the outer ring 28 is slidingly guided relative to the trunnion 15 by only the linear bearing interposed between the trunnion 15 and the outer ring 28, friction resistance is increased, and there may be caused a fear that the pressing force is not smoothly transmitted from the input-side disc 2 25 to the output-side disc 3. Because of this, there may also be caused a possibility that the pressing force becomes insufficient on the output-side disc 3 side.
On the other hand, in the construction disclosed in JP '249, since the flat surface portion which has to be machined with good accuracy is provided on both the trunnion 15 and the outer ring 28, there is caused a problem that the machining cost is increased. In addition, since a circulation mechanism of the roller bearing is difficult to be formed, it becomes difficult to realize a perfect rolling guide.
Furthermore, in the construction disclosed in JP '877, since the filter is mounted on the displacement shaft 23, it becomes difficult to secure a sufficiently large space as to mount the filer from the viewpoints of strength and rigidity, and hence, only a small filter can be mounted. Because of this, there is caused a fear that the filter is clogged early.
On the other hand, in the construction disclosed in JP '249 ,since the flat surface portion which has to be machined with good accuracy is provided on both the trunnion 15 and the outer ring 28, there is caused a problem that the machining cost is increased. In addition, since a circulation mechanism of the roller bearing is difficult to be formed, it becomes difficult to realize a perfect rolling guide.